Zeolites for reforming catalysts

ABSTRACT

Zeolites washed with aqueous solutions or water to exhibit pH in the range of 9.4 to 10.0 and preferably 9.6 to 10.0 which can be converted to reforming catalysts with enhanced activity, selectivity and activity maintenance. Also processes for washing the zeolite to the target pH range and processes for using catalysts made with the washed zeolite to reform naphtha feeds.

This is a division of application Ser. No. 259,644, filed Oct. 19, 1988,now U.S. Pat. No. 4,987,109.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to zeolite crystals, and preferablycrystals of large pore zeolites, such as zeolite L, which have beenwashed to a pH within the range of about 9.4-10.0, to processes foraccomplishing the desired zeolite washing, to catalytic reformingcatalysts based on washed zeolite crystals, and catalytic reformingprocesses which utilize catalysts based on washed zeolite. Catalyticreforming catalysts made from zeolite washed into the desired 9.4 to10.0 pH range exhibit activity, selectivity and activity maintenancewhich are significantly higher than catalysts using zeolites not washed.

2. Discussion of Background and Material Information

Catalytic reforming is a major petroleum refining process used to raisethe octane rating of naphthas (C6 to C11 hydrocarbons) for gasolineblending. Catalytic reforming is also a principle source of aromaticchemicals (benzene, toluene, and xylenes) via conversion of paraffinsand naphthenes to aromatics. The principle chemical reactions whichoccur during catalytic reforming include dehydrogenation of cyclohexanesto aromatics, dehydrocyclization of paraffins to aromatics,dehydroisomerization of alkylcyclopentanes to aromatics, isomerizationof normal paraffins to branched paraffins, dealkylation of alkylbenzenesand hydrocracking of paraffins to light hydrocarbons, i.e., methane,ethane, propane, and butane. The latter reaction is undesirable andshould be minimized since it produces light hydrocarbons not suitablefor gasoline blending which have less value than gasoline fractions.

Reforming is carried out at temperatures of 800° F. to 1000° F.,pressures of 50 to 300 psi, weight hourly space velocities of 0.5 to 3.0and in the presence of hydrogen at hydrogen to hydrocarbon molar ratiosof 1 to 10.

Reforming catalysts currently widely used in commercial reformers areplatinum on an alumina substrate, and platinum plus a second promotingmetal such as rhenium or iridium on alumina. These catalysts arebifunctional, i.e., the dehydrogenation reactions required in thereforming process are accomplished on the catalystic metal in thecatalysts and the isomerization and cyclization reactions also requiredin reforming are accomplished on strong acid sites on the aluminacatalyst support. Undesirable hydrocracking reactions which break C6+paraffins down to lower molecular weight hydrocarbons and reduceselectivity to aromatics occur on the strong acid catalytic sites.

Alumina based reforming catalysts demonstrate reasonably highselectivities for converting C8+ paraffins and naphthenes to aromaticsbut are less satisfactory for aromatizing C₆ to C₈ paraffins; theyhydrocrack more of the lower paraffins to low value fuel gas than theyconvert to aromatics.

New reforming catalysts are being developed which are significantly moreactive and selective for aromatizing C₆ to C₈ paraffins than aluminabased catalysts. These new catalysts are zeolite based rather thanalumina based. Zeolite based reforming catalysts are facile foraromatizing lower paraffins because they are monofunctional, i.e., theyaccomplish the isomerization reactions with great facility on the samecatalystic metal active sites as the dehydrogenation and cyclizationreactions. They do not require not contain strong acid sites whichpromote hydrogenolysis cracking reactions to accomplish isomerization.Moreover, certain zeolites have micropore dimension and configurationswhich sterically promote the desirable isomerization anddehydrocyclization reactions for C₆ to C₈ paraffins and repressundesirable hydrogenolysis cracking reactions. Accordingly, C₆ to C₈paraffin selectivity to aromatics is high for these sterically favoredzeolite catalysts. Zeolite which perform best as reforming catalystssubstrates fall into the so-called "large pore" category which have porediameters of 6 angstrom units or higher. The large pore zeolite L is aparticularly good reforming catalysts substrate.

U.S. Pat. No. 4,448,891, COHEN, is directed to an improved reformingcatalyst employing a zeolite L support provided by soaking the zeolite Lin an alkali solution having a pH of at least 11 for a time andtemperature effective to increase the period of time over which thecatalytic activity of the catalyst is maintained, wherein the procedureinvolves washing the alkali soaked zeolite with water followed byrepeated soakings in the zeolite solution for additional 18-hour periodswith washing repeatedly thereafter until the pH of the zeolite waterwash was at or below 10.5, followed by drying at 100° C.

U.S. Pat. No. 4,544,539, and 4,593,133, WORTEL, are directed to zeoliterelated to zeolite L having certain characteristics wherein the processfor preparation subsequent to separating the zeolite by centrifuging,involves washing four times with cold water prior to drying at 150° C.In one procedure, disclosed in WORTEL '539, zeolite crystals were washed5-6 times with cold water and the washings were decanted by centrifugingprior to drying in air for 16 hours at 150° C.

U.S. Pat. No. 3,216,789, BRECK, relates to a process for producingsynthetic zeolite which involves washing zeolite crystals, after thereactant mother liquor is filtered off, preferably with diluted water,until the effluent wash water, in equilibrium with the product, has a pHof between 9 and 12. This patent also discloses that as the zeolitecrystals are washed, the exchangeable cation of the zeolite may bepartially removed and is believed to be replaced by hydrogen cations. Ifthe washing is discontinued when the pH of the effluent wash water isbetween about 10 and 11, the (K₂ O+Na₂))/Al₂ O₃ molar ratio of thecrystalline product is disclosed as being approximately 1.0 but thatexcessive washing will result in a somewhat lower value for this ratio,while insufficient washing will leave a slight excess of exchangeablecations associated with the product.

SUMMARY OF THE INVENTION

The present invention is directed primarily to processes which involvewashing zeolite with a washing liquid, such as an aqueous solution orwater, and preferably deionized water, to produce zeolite crystalshaving a pH in the pH range of 9.4 to 10.0, and preferably within the pHrange of 9.6 to 9.8, and to zeolite crystals washed to within thedesired pH range.

Typically, washed zeolites, as recovered from the mother liquor in whichthey are crystallized, have a pH of about 12.5 so that they must bewashed with water or neutral pH water solutions to achieve the target9.6 to 10.0 pH range.

The preferred washing processes include slurrying the zeolite crystalswith water or appropriate wash solution and separating the crystals fromthe water in an appropriate filter, such as a pressure leaf filter,filter press or centrifuge. Then additional wash fluid is pumped intothe filter and through the deposited zeolite filter cake until thetarget pH range is achieved. The wash water can be pumped once throughthe zeolite filter cake and discarded.

Alternatively, a batch of wash water can be circulated through thefilter cake until steady state equilibrium is achieved between therecirculating batch of wash water and the zeolite filter cake, followingwhich the batch of wash water is discarded. If the resulting zeolite pHis too high the process is repeated with a fresh batch of wash water.

With all washing processes care must be taken that the batch of zeolitecrystals is washed uniformly to avoid variability in the resultingcatalyst. This usually requires that the cake of zeolite be depositeduniformly across the filter surface and that all sections of the filtersurface have equal access to wash fluid flow.

Another suitable washing process includes dislodging the zeolite filtercake into a vessel equipped with an agitator containing a charge of washfluid and slurrying the zeolite into the wash fluid. The zeolite iswashed until equilibrium is established between the wash fluid and thezeolite and then the zeolite is filtered out of the wash fluid. Thisprocess is repeated until the zeolite pH falls into the target range.

The present invention also relates to reforming catalysts produced fromthe properly washed zeolite by forming the washed zeolite intoaggregates using a suitable binder material such as alumina, silica,aluminosilicates, kaoline, and clays and incorporating appropriatecatalytically active metals, such as platinum, rhenium and iridium intothe catalyst by impregnation or ion exchange.

The present invention also relates to reforming processes which utilizethe catalysts produced form the appropriately washed zeolites. Onewidely practiced commercial reforming process utilizes a train of threeor four adiabatic packed bed reactors connected in series. The naphthafeed is vaporized and heated to 800° F. to 1000° F., mixed with hydrogenand fed into the inlet of the lead reactor. Reforming reactions are netendothermic so the temperature of the effluent from the reactors istypically below or in the lower end of the 800° to 1000° F. reformingtemperature range. Accordingly, reactor effluent streams are reheated infurnaces installed upstream of each of the reactors. The reactor productfrom the tail reactor is cooled and flashed to low pressure in a flashdrum and separated into a gas stream rich in hydrogen and into a liquidreformate product stream rich in aromatics. Part of the hydrogen streamfrom the flash drum is recycled into the feed stream entering the leadreactor to provide the hydrogen required to achieve the hydrogen to oilratio specified for the process. Reforming is a net hydrogen producingprocess so the balance of the flash drum overhead stream which containsthe hydrogen produced from the reforming reactions is sent off typicallyto a hydrogen purification unit to recover the hydrogen make.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be better understood and its advantages will becomemore apparent from the following detailed description, especially whenread in light of the attached drawing wherein the single figure is agraph showing the effect of zeolite pH on benzene yield as measured by acatalyst activity test, as defined herein.

DETAILED DESCRIPTION OF THE INVENTION

A primary objective of the present invention, therefore, is to produce azeolite reforming catalyst having superior activity, selectively andactivity maintenance. While the invention applies to any zeolite whichis a suitable substrate for reforming catalysts, the discussion hereinis directed to large pore zeolites and specifically zeolite L which wehave determined yields a particularly advantageous reforming catalyst. Acomplete description of zeolite L is provided in U.S. Pat. No. 3,216,789and procedures for making zeolite L are described in U.S. Pat. Nos.3,216,789 and 3,867,512, the disclosures of which are herebyincorporated in their entirety by reference thereto. We have discoveredthat reforming catalysts made using zeolites which have been washed withaqueous solutions or water such that the zeolite after washing exhibitsa pH in the pH range of 9.4 to 10.0, and preferably 9.6 to 9.8, can beconverted to reforming catalysts which exhibit superior performance.

For purposes of the present invention, the pH of the zeolite crystals isdetermined using the following procedure: a mixture of 10 grams ofzeolite and 100 grams of deionized water is stirred at room temperaturefor about five minutes and then centrifuged. The pH of the zeolite, asused herein, is the pH of the supernatent liquid determined using astandard pH meter calibrated with pH 7 and 10 buffer solutions.

The advantage of washing the zeolite to achieve the target zeolite pH isshown in the attached FIGURE in which reforming catalyst performance asmeasured by a standard catalyst activity test is plotted against the pHof zeolite L used to make the catalyst. Catalysts made with zeolitewashed to a pH, as defined above, with the pH range of 9.4 to 10.0, andpreferably in the 9.6 to 9.8 pH range, exhibit superior reformingcatalytic activity.

Although not wishing to be bound by any particular theory it is believedthat at pH greater than 10 the zeolite is underwashed such that too muchamorphous silicate and aluminate residue from crystallization remain inthe zeolite. These detrimental residues block access to the zeolitemicrochannels in which the reforming reactions occur interfering withthe reactions. At pH below 9.4 the zeolite has ben overwashed such thatan excessive fraction of exchangeable potassium ions in the zeolite arereplaced by hydrogen ions from the wash water. This introducesundesirable excess acidity which in turn induces hydrogenolysis crackingof feed when the zeolite is converted to a catalyst and used in areforming process.

Accordingly, to produce reforming catalysts with optimal activity,selectivity and activity maintenance it is necessary to control the pHof zeolite crystals used to make the catalyst to the pH range of 7.4 to10.0, and preferably 9.6 to 9.8.

This is accomplished by passing an aqueous washing fluid over thezeolite crystals until the desired pH is achieved. The washing liquidmay be made preferably with deionized water to insure that nocontaminants are added by the zeolite which could impair performance ofcatalysts produced with its zeolite.

Alternatively, the washing fluid could contain salts or bases of theprinciple exchangeable cations in the zeolite to reduce ion exchangereplacement of zeolite cations with hydrogen in the wash water.

In accordance with the present invention, therefore, uniform washing ofzeolite crystals with liquid is accomplished by first depositing thezeolite crystals on a barrier surface preferably in a substantiallyuniform layer. In general, any barrier surface on which the zeolitecrystals will be retained while permitting the passage of the washingliquid therethrough is suitable for purposes of the present invention.Thus, the process of the present invention can be performed using anyconventional filter or thickener apparatus suitable for this purpose. Inthis regard, suitable results have been achieved in accordance with thepresent invention using a pressure leaf filter, such as a Funda filter.A multi-plate thickener, such as a continuous thickener commerciallyavailable from T. Schriver Co. or a plate and frame filter press mayalso be employed. In any case, however, the barrier surfaces, such asfilter cloths or screens, are preferably made of stainless steel orpolypropylene material, although the only requirement for purposes ofthe present invention is that the material must be able to withstand ahigh pH of about 10.0.

Although there are several suitable processes to wash zeolite crystalsin accordance with the present invention, the preferred process is onewherein the zeolite crystals are separated from the mother liquor usinga pressure leaf filter, i.e. a Funda filter, and then pumping freshlysupplied aqueous liquid, such as deionized water, through the zeolitefilter cake until the pH of the zeolite reaches the prescribed pH rangeas described in more detail herein. Typically, about 4 gallons of washwater per pound of zeolite are pumped through the filter to reduce thepH to the target range. In this embodiment it is particularly importantto insure that the zeolite crystals are uniformly deposited across thefilter surface to avoid maldistribution of wash water flow through thezeolite crystals so that all segments of the batch are washed uniformly.

For this purpose it is preferred to precoat the filter screen with afilter aid to promote uniform laydown of zeolite on the screen andreduce loss of smaller zeolite crystals. It is preferred to precoat thebarrier surface with an inert material having substantially the samecomposition as the inorganic binder material ultimately used inproducing the catalyst containing the washed zeolite powder. Therefore,it is preferable to select a material from the group of alumina, silica,alumina-silica, kaolin, or other clay depending upon which of thesematerials will be ultimately used in the manufacture of the catalysts.

Although the zeolite material useful for the purposes of the presentinvention may be selected from the group consisting of large-porezeolites, type L zeolite are preferred. Representative examples ofpreparing type L zeolite suitable for purposes of the present inventionare described in U.S. Pat. Nos. 3,216,789 and 3,867,512 in addition toU.K. Application No. 82-14147, the disclosures of which are incorporatedherein by reference.

As previously mentioned, type L zeolite is preferred catalyst, supportor base materials for purposes of the present invention. As used herein,the term "zeolite" refers to a group of naturally occurring, hydrated,metal aluminosilicates, which are crystalline in structure in additionto synthetic zeolite having a composition similar to certain of thenatural crystalline zeolites. For purposes of the present invention, theterm "zeolite L" and "type L zeolite" are used interchangeable and referto synthetic zeolite. By way of further explanation, type L zeolites aresynthetic zeolites which crystallize in the hexagonal system with acharacteristic X-ray diffraction spectrum, i.e. a characteristic X-raydiffraction pattern obtained from CuK alpha radiation with the majord(angstrom) peak values set out in Table A.

                  TABLE A                                                         ______________________________________                                        16.10 ± 0.3 3.91 ± 0.02                                                                          2.91 ± 0.01                                       7.52 ± 0.04 3.47 ± 0.02                                                                          2.65 ± 0.01                                       6.00 ± 0.04 3.28 ± 0.02                                                                          2.46 ± 0.01                                       4.57 ± 0.04 3.17 ± 0.01                                                                          2.42 ± 0.01                                       4.35 ± 0.04 3.07 ± 0.01                                                                          2.19 ± 0.01                                       ______________________________________                                    

A theoretical formula is M₉ /n[(AlO₂)₉ (SiO₂)₂₇ ]. The real formula,however, may vary by, for example, the ratio of silicon to aluminumvarying from 2.5 to 3.5. A general formula for zeolite L may berepresented as follows:

    0.9-1.3M.sub.2 O:Al.sub.2 O.sub.3 :xOSiO.sub.2 :yH.sub.2 O

wherein 37 M" designates at least one exchangeable cation; "n"represents the valence of "M"; and "y" may be any value from 0 to about9, and "x" is any value between 5.01 and 7.0 and preferably between 5.2and 6.9.

Thus, type L zeolites with SiO₂ /Al₂ O₃ ratios less than 5.2 or greaterthan 6.9 are applicable to this invention. Preferably, the SiO₂ /Al₂ O₃ratio may vary between about 2 and about 50. For example, one method ofreducing the SiO₂ /Al₂ O₃ ratio involves leaching some of the SiO₂ withan akali metal hydroxide, e.g., KOH, to produce type L zeolite useful inthis invention. Physically, zeolite-L has channel-shaped poresundulating from about 7 to 13 angstrom in diameter and may occur in theform of cylindrical crystals with a mean diameter of at least 0.5 micronand an aspect ratio of at least 0.5. The above notwithstanding, minorvariations in the mole ratios of the oxides within the ranges indicatedby the above formulas do not significantly change the crystal structureor physical properties of the zeolite.

As previously discussed, zeolite L can only be synthesized in thepotassium form, i.e., in a form in which exchangeable cations presentare substantially all potassium ions. But the cations are exchangeableso that zeolites may be formulated to contain a number of cations suchas mono-, di- and trivalent metal ions, particularly those of Groups I,II and III of the Periodic Table including barium, calcium, cesium.lithium, magnesium, potassium, sodium, strontium and zinc ions and thelike in addition to other cations, for example, hydrogen and ammoniumions. For example, a type L zeolite in potassium form can be ionexchanged by treatment with an aqueous solution containing a rubidiumand/or cesium salt, after which the zeolite is washed to eliminateexcess ions. The percent of ions exchanged can be increased by repeatingthe ion exchange treatment of the zeolite.

Inasmuch as crystallized, zeolite particles are extremely fine in size,typically about one micron, they are difficult to contain in a fixed bedreactor and would induce extremely high pressure drops. The zeolitecrystals, therefore, are preferably formed into aggregates, such asextrudates, tablets, pills or spherical forms, typically, in the 1/32 to1/4 inch size range, to be suitable for use in commercial fixed bedreactors. In this regard, inorganic binder such as alumina, silica,kaolin or an alumina-silicate is required to hold the aggregate togetherand provide crush strength and attrition resistance. Methods for formingzeolite L aggregates are disclosed in U.S. Pat. Nos. 4,595,668 and4,648,960.

To complete the production of the zeolite based reforming catalyst oneor more catalytically active metals must be dispersed into the zeolite.These metals are typically Group VIII metals which include platinum,rhenium and iridium. Other metals can be added to promote the activityand stability of the catalyst. These include tin, iron, germanium andtungsten. Platinum can be introduced by impregnating either the zeolitecrystals prior to forming the aggregates or the aggregate zeoliteparticles with an aqueous solution of a platinum salt or complex such aschloroplatinous acid, hexachloroplatinic acid, dinitrodiaminoplatinum orplatinum tetraamine dichloride. Alternatively, platinum can beintroduced by ion exchange with potassium ions in zeolite L using a saltsuch as platinum tetraamine dichloride. Similar compounds can e used tointroduce other metals such as rhenium and iridium into the zeolitecatalyst. We have determined that superior catalysts are obtained whenat least 90% of the metals added to the catalyst prior to reduction areless than 7 angstrom units in size.

Conventional techniques used to manufacture catalysts are disclosed inU.S. Pat. Nos. 4,595,668 and 4,648,960, the disclosure of which ishereby incorporated by reference thereto. Catalysts ofplatinum-potassium type L-zeolite have been disclosed in U.S. Pat. No.4,552,856, TAUSTER et al., the disclosure of which is herebyincorporated by reference thereto herein. U.S. Pat. No. 3,557,024 YOUNGet al., disclose alumina bound catalysts having a composition formed bymixing one of a number of zeolites, including zeolite-L, with a binderof hydrous boehmitic alumina, the disclosure which is herebyincorporated by reference thereto.

The following discussion is an elaboration of the invention applied topotassium zeolite L. However the inventive concepts apply equally toother zeolites.

The washing process begins after the zeolite crystallization iscomplete. Zeolite l is crystallized out of a gel containing potassiumhydroxide, silica, alumina and water. (Potassium is required in the gelbecause zeolite L crystallizes only in the potassium form, e.g., theexchangeable cations in the zeolite are potassium.) The residual zeoliteand crystallization mother liquor are basic, typically in the 12 to 13pH range. The mother liquor is drained out of the crystallizer and thezeolite is reslurried in water, preferably deionized water. The zeoliteslurry is pumped into a filter in which the zeolite is deposited on afilter screen. Appropriate filters include pressure leaf filters such asthe Funda filter, plate and frame filter presses and centrifuges.Stainless steel and polypropylene filter screens can be employed withgood effect but other materials can also be used. Whichever filtrationsystem is used it is important to lay down the zeolite filter cakeuniformly across the filter surface to insure that all elements of thefilter cake are thoroughly washed.

A preferred washing mode is to pump fresh water into the filter andthrough the zeolite filter cake through the filter screen until thezeolite exhibits a pH in the target 9.4 to 10.0 range. Typically, about4 gallons of wash water per pound of zeolite have to be pumped throughthe filter to reduce the pH to target range.

Although the wash liquid or fluid we prefer to use is simply water, andpreferably deionized water to insure that no contaminants are addedwhich could interfere with the performance of catalysts madesubsequently with the zeolite, we have also successfully used aqueouswater solutions, such as potassium solutions. Of course the pH of thesesolutions must be below the 9.6 to 10.0 target pH to reduce the pH intothe target range. The rationale for using potassium solutions ratherthan water to wash the zeolite is to repress exchange of hydrogen ionsfor potassium ions in the zeolite L which we believe is deleterious tocatalyst performance.

The preferred washing process is simply to pump wash water through thezeolite until the zeolite pH falls into the target range, however, otherwashing modes have been successfully tested. One such mode is torecirculate a charge of wash water, typically one gallon of wash waterper pound of zeolite, around through the filter several times to achieveequilibrium between the zeolite and the wash water. This operation isrepeated until the zeolite pH falls into the target range; typicallythree or four charges of water are required. Another operating mode isto recirculate a charge of wash water through the filter and continuallyreplace part of the recirculating water stream with fresh water. Stillanother washing process is to dislodge the filter cake into a charge ofwash water in a vessel equipped with an agitator. The zeolite batch isslurried and washed in the water for a period of time and then separatedfrom the wash water in the filter. This operation is repeated until thezeolite pH falls into the target range.

We prefer to precoat the filter screen with a filter aid to promoteuniform laydown of zeolite on the screen and reduce loss of smallerzeolite crystals. The preferred filter aid is the binder which will beused subsequently to form the zeolite crystals into an aggregatesuitable for use in commercial fixed bed reactors. Suitable bindersinclude alumina, silica, kaolin, and alumina-silicates.

As previously discussed, zeolite L is synthesized in the potassium form.Although potassium zeolite L is an excellent substrate for reformingcatalysts, good reforming catalysts can also be produced using zeolite Lin which some potassium ions are exchanged for other cations. Suitablecations for zeolite L reforming catalyst substrates include barium,calcium, cerium, lithium, magnesium, sodium, strontium, and zinc. If itis desired to introduce an additional cation into the zeolite, a salt ofthat cation could be added to the wash solution and the ion exchangeaccomplished simultaneously with washing. Alternatively, anotherconvenient point in the processing sequence to accomplish the ionexchange is immediately after the zeolite L is washed to target pH.

EXAMPLE I Illustrating Advantage of Washing Zeolite to Target 9.4 to10.0 pH range

An accelerated 24 hour activity test has been developed which accuratelyrates the activity of zeolite reforming catalysts on a relative basis.The activity test is conducted at 950° F. at space velocity of 8.0w/w/hour based on zeolite in the catalyst and 4.25 molar hydrogen to feeration. The feed is 40% normal hexane and 60% methylpentanes by weight.The catalyst performance index is simply the weight percent benzeneyield on feed after 23 hours at test conditions.

The previously described activity test was employed to demonstrate theadvantage of the zeolite was procedure of this invention by comparingthe performance of a series of reforming catalysts which are identicalin all respects except that the zeolites in the different catalysts werewashed to different pH's as determined by the procedure previouslydescribed.

The relevant data as presented in Table 1 as follows:

                  TABLE 1                                                         ______________________________________                                        REFORMING CATALYST PERFORMANCE                                                VERSUS ZEOLITE pH                                                                      Benzene Yield                                                        Zeolite pH                                                                             at Hrs, Wt %                                                                              Comments                                                 ______________________________________                                        9.9      49.6        Slightly Under-Washed Product                            10.2     44.3        Under-Washed Product                                     9.8      51.3        Properly Washed Product                                  9.7      51.1        Properly Washed Product                                  9.7      49.6        Properly Washed Product                                  9.6      50.9        Properly Washed Product                                  9.8      51.2        Properly Washed Product                                  9.6      50.5        Properly Washed Product                                  9.6      50.9        Properly Washed Product                                  9.0      41.0        Over-Washed Product                                      10.4     39.6        Under-Washed Product                                     ______________________________________                                    

The catalysts for these runs were prepared using the followingprocedure: Thirty gram lots of washed potassium zeolite L powder weredried under vacuum at 150° C. for 16 hours yielding 21.6 grams of driedzeolite L crystals. Into this powder 14.256 grams of an aqueous solutioncontaining 0.1647 grams of Pt(NH3)₄ C1₂ -H2O (Pt assay 55.4 wt. %) and14.0913 grams of water was added. The resultant mixture was convertedinto a uniform paste which was allowed to stand at room temperature forabout 30 minutes and then dried at 110° C. for four hours. The driedpaste was then formed into a pellet and then broken and sieved torecover particles in the 20 to 45 mesh size range. The catalystparticles were dried at 480° C. in air for three hours and then treatedunder hydrogen at 510° C. for one hour to reduce the platinum to thezero valent metal state just prior to initiating the acceleratedactivity test.

Catalyst made with zeolite washed to within the desirable pH range of9.4 to 10.0 exhibited activities of 50 wt. % benzene. In contrast,underwashed zeolite, exhibiting a pH above the target pH range at 10.4,converted to catalyst which demonstrated only 40 wt. % benzene yield inthe standard activity test. Overwashed zeolite, exhibiting a pH belowthe target pH range at 9.0, converted to catalyst which demonstratedonly b 41 wt. % benzene yield in the standard activity test. Theadvantage of washing the zeolite to the specified 9.4 to 10.0 pH rangeis clearly indicated.

EXAMPLE II Illustrating How a Batch of Zeolite was Washed to 9.5 to 10.0pH Range

A slurry containing 10 to 20 wt. % of zeolite L was produced by drainingcrystallization mother liquor from a recently synthesized batch of thezeolite and then mixing the resulting cake into deionized water. Thezeolite was separated from the water in a Funda filter. The zeolite Lwas synthesized in accordance with the procedure set forth in Example 1of U.S. Pat. No. 4,544,539. The Funda filter is a commercial horizontalplate filter containing 43 circular filter plates mounted in a verticalstack on a central shaft in a cylindrical pressure vessel. The centralshaft/filter plate assembly can be spun to dislodge the filter cake. Thefilter vessel volume is 1000 gallons and the filter screen surface areais 900 square feet. The filter screen material used in this example waspolypropylene.

The zeolite slurry was pumped into the Funda filter until the filter wasnearly full. The initial pH of the zeolite L as it was pumped into thefilter was 12.5. About 1500 lbs. of zeolite (dry basis) was contained inthe slurry charged to the filter. The zeolite was deposited uniformly onthe filter screen plates by forcing water in the slurry through thefilter screen and out of the filter via a conduit in the shaft of thefilter press by raising the air pressure above the slurry. The Fundafilter was then filled with deionized water. Next a flow of freshdeionized water heated to 150° F. was initiated into the filter at arate of 20 gallons per minute. The water flowed through the zeolitecake, through the filter screens and out of the filter via the shaftconduit to sewage. After total of 4783 gallons of deionized water waspumped through the filter, the flow of wash water was stopped. Water inthe Funda filter was pressured through the zeolite filter cake and outof the filter using air pressure and the wash water heel remaining inthe bottom of the filter was drained to sewage.

Samples of washed zeolite were taken from several of the filter platesand were removed from the filter through manholes in the side of thefilter vessel. The pH of these zeolite samples were determined by themethod described previously and all the samples were in the 9.6 to 10.0target pH range. The filter cake was dried to about 30 wt. % watercontent by passing air at 150° F. through the filter over the zeolitefor eight hours. The cake was then dislodged from the filter screen byspinning the filter central shaft assembly and dumping the zeolite outthrough a port in the bottom of the filter.

EXAMPLE III Illustrating How Washed Zeolite was Converted Into aReforming Catalyst

The zeolite powder was formed into 1/32 inch extrudate using thefollowing procedure: for each 100 lbs. of zeolite, 10 lbs. of bohemitealumina was mixed with 105 lbs. of acidic alumina water sol containing20% alumina in a Muller type mixer. The zeolite was added to the mixerand kneaded into a paste. The paste was heated in the mixer until itswater content was reduced to 32 wt. %. The paste was then extruded into1/32 inch diameter extrudate using a four inch conventional single screwextruder and the resulting extrudate broken into particles in the rangeof 1/32 to 1/4 inch in length. The extrudate was dried at 150° C. andcalcined at 500° C.

Platinum was loaded into the extrudate using the following procedure: asolution having the composition 2.4321 grams Pt(NH3)₄ Cl₂.H2O, 1.822grams KC1, 1.2 grams KOH and 354.55 grams H2O was circulated for 30minutes at 20° C. over 200 grams of the zeolite extrudate. The loadingsolution was drained from the extrudate and the wet extrudate wasmaintained at 50° C. for 20 hours. The extrudate was dried at 110° forfour hours and calcined in air at 350° C.

EXAMPLE IV Illustrating Performance of Reforming Catalyst Made UsingZeolite Washed to Target 9.4 to 10.0 pH Range

The catalyst made using the preceding procedure was charged into a pilotplane reforming reactor system which included four one inch i.d.reactors piped in series and operated so as to closely simulate acommercial reforming unit.

                  TABLE IV                                                        ______________________________________                                        Run Data                                                                      Reactor inlet T, °F.                                                                        950    968    968  968                                   Reactor outlet T, °F.                                                                       869    876    880  919                                   ______________________________________                                        Feed composition:                                                                    Component                                                                             wt %                                                           ______________________________________                                               C.sub.5 0.14                                                                  NC.sub.5                                                                              0.43                                                                  CP      0.0                                                                   22 DMB  0.96                                                                  23 DMB  3.47                                                                  2MP     19.22                                                                 3MP     21.80                                                                 NC.sub.6                                                                              34.94                                                                 C.sub.6.sup.-                                                                         0.03                                                                  MCP     4.86                                                                  CH      0.43                                                                  Bz      0.02                                                                  IC.sub.7                                                                              13.16                                                                 NC.sub.7                                                                              0.34                                                                  C.sub.7.sup.-                                                                         0.00                                                                  DMCP    0.18                                                                  MCH     0.01                                                                  TOL     0.00                                                                  C.sub.8.sup.+                                                                         0.01                                                                  Total   100.0                                                                 C.sub.5.sup.- + DMB:                                                                  5.00                                                                  C.sub.6 's:                                                                           81.30                                                                 C.sub.7 's:                                                                           13.70                                                                 Total S:                                                                              <10 ppb                                                        ______________________________________                                        Operating Conditions                                                          Space Velocity       2.0 WHSV-1.56 WHSV                                       Hydrogen/Oil Ratio   4.5 H.sub.2 /oil molar                                   Hydrogen Partial Pressure                                                                          98 psia                                                  ______________________________________                                        Total catalyst weight 300 g                                                   distributed as follows:                                                                      Cat.                                                                  Reactor Dist. Wt.                                                      ______________________________________                                               1       14                                                                    2       18                                                                    3       34                                                                    4       34                                                             ______________________________________                                        Product Yield                                                                 At 300 hours into run on oil:                                                 C.sub.6 plus conversion                                                                            73.9 wt % on feed                                        Aromatic yield       41.8 wt % on feed                                        Selectivity to aromatics                                                                           58.3 wt % on feed                                        ______________________________________                                    

As in the above data shows, the catalyst made using zeolite washed tothe specified 9.6 to 10.0 pH range as specified in this inventionperformed admirably in the reforming test. In particular, the highselectivity and yield achieved converting C6's and C7's to aromatics arevery impressive.

Although the invention has been described with reference to particularmeans, materials, embodiments, and examples, from the foregoingdescription, one skilled in the art can easily ascertain the essentialcharacteristics of the present invention, and various changes andmodifications may be made to adapt to various usages and conditions,without departing from the spirit and scope of the invention asdescribed in the claims that follow.

What is claimed is:
 1. A reforming process for a hydrocarbon feedstockcomprising:contacting said hydrocarbon feedstock at reforming conditionswith a catalyst comprising zeolite containing exchangeable cationsloaded with at least one catalytically active metal selected from thegroup consisting of Group VIII metals of the Period Table of Elements,tin and germanium, said zeolite having a pH of 9.4 to 10.0 determined bymeasuring pH of supernatant liquid from a mixture of one part of zeolitecrystals with ten parts of deionized water by weight, and said zeolitebeing present in an amount effective to enhance the activity,selectivity and activity maintenance of the catalyst, so as to increasearomatics content and octane rating of said hydrocarbon feedstock. 2.The reforming process in accordance with claim 2 wherein said pH iswithin the range of 9.6 to 9.8.
 3. The process in accordance with claim1, wherein said exchangeable metal cations selected from the groupconsisting of potassium, sodium strontium, barium, calcium, lithium,magnesium, rubidium, and cesium.
 4. The reforming process in accordancewith claim 1, wherein said zeolite is a large-pore zeolite.
 5. Thereforming process as defined by claim 4, wherein said large-pore zeoliteis zeolite L.
 6. The reforming process as defined by claim 5, whereinsaid cation is potassium.
 7. The reforming process as defined by claim1, wherein said catalytically active metal is a Group VIII noble metal.8. The reforming process as defined by claim 7, wherein said Group VIIInoble metal is Pt.
 9. The reforming process as defined by claim 7,wherein said Group VIII noble metal comprises particles having a meanapparent diameter of no more than about 7 Angstroms.
 10. The reformingprocess as defined by claim 4, wherein said catalyst further comprises aco-catalyst selected from the group consisting of Re, Ir, W, Sn, and Fe.11. The reforming process as defined by claim 10, wherein saidco-catalyst is selected from the group consisting of Re and Ir.
 12. Thereforming process as defined by claim 4, wherein said catalyst furthercomprises an inorganic binder selected from the group consisting ofsilica, alumina, silica-alumina, and kaolin.
 13. The reforming processas defined by claim 12, wherein said catalyst is an aggregate.
 14. Thereforming process as defined by claim 13, wherein said aggregate isselected from the group consisting of extrudates, tablets, pellets andprills.